The primary goal of this research is to gain a better understanding of the mechanisms through which cellular interactions influence gene expression in the developing central nervous system. Bergman glia cells in the mouse cerebellum express high levels of the enzyme, sn-glycerol-3-phosphate dehydrogenase (GPDH), beginning shortly after birth. Based largely on observations of GPDH expression in certain neurological mutant mice, it appears that the characteristic pattern of GPDH expression in the Bergman glia depends upon an early and sustained interaction between those cells and adjacent Purkinje neurons. Because of the unique combination of specific biochemical, genetic and molecular approaches available, this system constitutes a particularly appropriate model of a common but not well understood developmental phenomenon. The proposed studies will test several hypotheses concerning Purkinje cell/Bergman glia interactions: 1. To determine whether interaction with Purkinje cells regulates GPDH levels in Bergman glia by influencing specific messenger RNA expression, in situ hybridization with cDNA probe will be used to assess message levels in animals showing reduced enzyme levels; 2. To determine whether there is a restricted critical period during which Purkinje cells can influence glial GPDH expression, local intracerebellar injection of specific neurotoxic agents will be used to kill Purkinje cells at varying ages from 4 to 12 weeks postnatal. GPDH expression around the injection site will be assessed GPDH expression following the death of Purkinje cells remain competent to reexpress the enzyme, normal, fetal Purkinje cell precursors will be implanted into cerebella of adult Lurcher mutant mice. GHDH expression in the region surrounding the implant will be monitored immunocytochemically 2 to 12 weeks post implantation. Electron microscopic analysis of implants will also be performed to assess the structural relationship that develops between host Bergman glia and the implanted Purkinje cells; 4. Finally, two different cell culture model systems will be used to determine whether the Purkinje cells influence on glial enzyme expression is mediated by direct cell-cell contact. Enzyme expression in monolayer cultures normally remains low, presumably due to the lack of Purkinje cell survival and the minimal amount of appropriate cell-cell contacts in this system. Thus, Purkinje cell-enriched membranes will be tested for ability to stimulate GPDH expression in Bergman glia in monolayer cultures. Alternatively, this question can be approached using reaggregating cell cultures, where GPDH expression shows the same pattern and time course as in vivo. Experiments are planned to follow up on observations that suggest certain tumor cell membranes can inhibit GPDH expression in reaggregating cultures. It is expected that these studies will lead to the biochemical characterization and purification of cell surface-associated molecules involved in regulating glial enzyme expression.